This application claims the priority of Austrian Patent Application Serial No. GM 146/2000, filed Mar. 3, 2000, the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to a drill bit, such as a Forstner bit or machine bit, and more particularly to a drill bit of a type having a shank and a cutting head which has a central center point and first and second cutting edges extending radially outwards from opposite sides of the center point.
Drill bits of this type are mass products for use in hand drills, drill presses, tap borers, or gang drilling machines, and produced in great numbers for commercial purposes. Holes of relatively great diameter can be drilled in a wide variety of materials such as plastic-coated chipboards, bonded wood panels, acrylic glass plates and other base materials. Conventional drill bits suffer, however, shortcomings because drilling machines are required to apply relatively high drilling forces and torques as the cutting edges must overcome with their straight edges high material resistance.
It would therefore be desirable and advantageous to provide an improved drill bit to obviate prior art shortcomings and to increase the efficiency of the drilling process by reducing drilling forces to be applied.
The present invention provides for a drill bit which includes a shank, and a cutter head connected to the shank and having a central center point and first and second cutting edges extending radially outwards from opposite sides of the center point, with the first and second cutting edges so formed along their radial extension with valleys and peaks in alternating disposition that in relation to the center point, as viewed in radial direction, the valleys of the first cutting edge are arranged at locations where the peaks of the second cutting edge are disposed, and the peaks of the first cutting edge are arranged at locations where valleys of the second cutting edge are disposed.
Through the provision of a repeating patterns of peaks and valleys in staggered relationship on the opposite cutting edges, the cutting force to be applied is divided, whereby the peaks of each cutting edge effect concentric, circular cutting tracks around the center point, while the offset disposition of the of peaks and valleys on the other cutting edge produces exactly the cutting tracks in-between. As a result, an overall even borehole is realized, while each cutting edge provides only half of the entire cutting energy. In this manner, the drilling procedure can be implemented at smaller drilling force and smaller torque.
According to another feature of the present invention, the peaks and valleys are formed by chip breaker profile, wave-shaped profile, knurled profile or similar teeth formation. The offset disposition of the peaks and valleys on both cutting edges leads in the wave-shaped profile, chip breaker profile, or knurled profile to the desired effect of reducing the drilling force. Depending on the material, a modification of the arrangement of the peaks and valleys provides an optimum cutting performance.
According to another aspect of the present invention, two bar-shaped cutting edges are arranged in 90xc2x0 offset disposition to the first and second cutting edges on the circumference of the center point, thereby facilitating a centering of the drill bit during the drilling procedure and ensuring a precise drilling action.
According to another feature of the present invention, at least one of the peaks may have a tapered cross section in radial extension, as viewed in opposition to a rotation direction of the drill bit, and at least one of the valleys may have a widening cross section in radial extension, as viewed in opposition to a rotation direction of the drill bit. As a consequence of this configuration, the flanks of the peaks are prevented from touching the workpiece, thereby reducing friction and accompanying heat generation during the drilling procedure. In addition, this configuration permits a higher rotation speed and/or feed rate during the drilling procedure as the drill bit encounters less resistance from the material.
According to another aspect of the present invention, the at least one of the peaks may be configured in symmetry to its center line. The center line extends substantially in circumferential direction. The symmetric configuration of the peak likewise reduces the friction on the flanks on both sides of the peak. Suitably, the at least one peak evenly tapers in opposition to a rotation direction of the drill bit and defines flanks, with each of the flanks extending at a constant angle with respect to a normal to the cutting edges, whereby the valleys are configured as a part of a hollow cylinder or hollow truncated cone. As a consequence of the constant angle, the valley may be realized through milling with slanted milling axis, thereby keeping production costs to a minimum. It is further contemplated that the constant angle may range from 3xc2x0 to 7xc2x0, preferably from 4xc2x0 to 6xc2x0. This selection ensures that the friction of the flank of the peak is reduced and an excessive weakening of the peak is avoided.